Electronic control systems associated with motor vehicle powertrains utilize certain data for performing control functions. Some data that is processed by control algorithms to develop control data is obtained directly from sensors while other data used by control algorithms is developed by processing certain data according to various other algorithms. Because driving conditions frequently change during typical trips made by a motor vehicle, data that is used by control algorithms must be updated with sufficient regularity to accurately reflect changes, and processing performed by an electronic control system must be fast enough to keep pace with changing conditions in order to assure optimal vehicle performance. Transients in engine/powertrain operation are especially challenging for control systems.
Because of particular dynamics of particular engine/powertrain components and/or the manner in which data for, or related to, them is developed, certain data that is important for optimal vehicle performance may not track operational changes, especially transients, with sufficient timeliness for optimal vehicle performance as those changes are occurring.
For example, shifting of an automatic transmission may be controlled by the amount of engine brake torque being produced by an internal combustion engine. When control of transmission shifting is electronic in nature, a processing system must develop accurate engine brake torque data for use by an automatic transmission controller to assure shifting at the proper time. Because shifting occurs as a consequence of the vehicle being accelerated or decelerated, the powertrain is in a dynamic state, and so is data related to it.
A known processing strategy for calculating engine brake torque data during transient operation, such as during engine acceleration, uses engine rotational inertia data and engine speed change (acceleration) data to compensate basic torque data that is being calculated according to what is essentially a steady-state algorithm. While the iteration rate of the steady-state algorithm, in conjunction with compensation for acceleration transients, might seem sufficiently fast to yield accurate brake torque data as the engine speed changes, various factors, such as component dynamics, affect accuracy and lead to the need for even better transient compensation.
One of the present inventor's prior patents, U.S. Pat. No. 6,584,391, relates to a system and method for engine torque calculation. The algorithm that is embodied in that system and method calculates gross engine torque by processing engine speed and fueling data. Net torque, i.e. brake torque, is calculated by calculating torque losses and subtracting those losses from calculated gross torque.
One component of torque loss is engine pumping loss, which is a function of different factors that include intake manifold pressure and exhaust backpressure. When the engine accelerates, an engine speed derivative term calculation contributes to transient compensation for engine torque.
In certain motor vehicles having turbocharged engines and automatic transmissions whose shift points are electronically controlled, it has been observed that shift quality may be affected by the nature of certain turbochargers, such as certain two-stage turbochargers. Through recognition that the quality of transmission shifts is attributable to the effect of such turbochargers on the prior method for brake torque calculation, the inventors have created a novel and improved strategy for calculating engine brake torque.